Blender Loop cuts and vertices measurement
Blender doesn't offer exact dimension modelling tools that you may expect in a CAD program. There are some things that may help, start with this previous question.

Most tools allow you to type in numeric values while they are being applied, what that value represents may vary between tools. When using the loop cut tool you can enter a value between 1.0 and -1.0 that represents a percentage of movement towards the next vertex on either side with 0.0 being centred.

Extruding allows you to enter a length that is a distance from the original location. You can also cancel the extrude to leave the new vertices in the same location as the original vertices, then move the vertices (G) which allows you to enter x,y,z values as distance moved in each direction. The first number you enter is used for x then you can use tab to move to the y and z values.

Pressing Ctrl and Shift can also help - while you are moving vertices pressing Ctrl is a shortcut to enable snapping which by default will snap values to whole units (grid increment snapping type). Pressing Shift will slow down the movement to allow more precise placement. Pressing Ctrl and Shift will snap to 0.1 increments.

With loop cut Ctrl will snap to 0.1 increments, Shift will slow down movement and together will snap to 0.01 increments.